Thank you for your help so far. A couple more questions -


What should I look for in a vacuum pump to determine if it may be the cause of the knocking?

When I cycle the motor by hand I get this wired creaking sound (like an old box spring) but only seems to be on exhaust stroke for #1 and #2??? Otherswise I do not see, feel or hear any other strange noices...
Any ideas as to what that might be????